A gunman who ran amok at a church youth performance killed two people, including an usher described as a hero for shielding others from the blast.

Members of the Tennessee Valley Unitarian Universalist Church dived under pews or ran from the building in Knoxville yesterday when the shooting started.

The man, armed with a shotgun, was tackled by congregants and eventually taken into police custody. None of the children was injured.

A hospital spokeswoman said seven people were injured and five were in critical or serious conditions.

Jim Adkisson, 58, was charged with first-degree murder, said city spokesman Randy Kenner.

Authorities were searching his home in the Knoxville bedsit community of Powell.

The murdered usher was Greg McKendry, 60, a long-time church member.

The second shooting victim, 61-year-old Linda Kraeger, died from her injuries hours later.

Congregation member Barbara Kemper said Mr McKendry "stood in the front of the gunman and took the blast to protect the rest of us".

The gunman's motive was not yet known.

The church, like many other Unitarian Universalist churches, promotes progressive social work, such as desegregation and fighting for the rights of women and gays. The Knoxville congregation has provided sanctuary for political refugees, fed the homeless and founded a chapter of the American Civil Liberties Union, according to its website.

Ms Kemper said the gunman shouted before he opened fire.

"It was hateful words. He was saying hateful things," she said, but refused to elaborate.

The FBI was assisting in the case, Police Chief Sterling Owen said, in case it was a hate crime.

There were about 200 people watching the performance by 25 children when the shooting took place.

Church member Mark Harmon, who was was in the first row, said: "It had barely begun when there was an incredibly loud bang."

Mr Harmon said he thought the noise was part of the play, then he heard a second loud bang. As he dived for cover, he realised a woman behind him was bleeding and appeared to be in shock, touching her wound.

"It seems so unreal," he said. "You're sitting in church, you're watching a children's performance of a play and suddenly you hear a bang."

Harmon said church members just behind him in the second and third rows were shot. He said his wife told him that she saw the gunman pull the shotgun out of a guitar case.

Witnesses reported hearing about three blasts from the 12-gauge shotgun, which spreads pellets out when the shot leaves the barrel. Witnesses said they did not recognise the gunman.